It is known that cured silicone powder can be prepared by curing liquid particles of a curable silicone composition comprising a platinum catalyst, an organopolysiloxane having at least two silicon-bonded alkenyl groups in each molecule, and an organopolysiloxane having at least two silicon-bonded hydrogen atoms in each molecule.
For example, Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 62-243621 (243,621/1987)/U.S. Pat. No. 4,742,142, teaches a process in which (i) a curable silicone composition comprising a platinum catalyst, an organopolysiloxane having at least two silicon-bonded alkenyl groups in each molecule, and an organopolysiloxane having at least two silicon-bonded hydrogen atoms in each molecule, is emulsified using water and a surfactant; and (ii) the curable silicone composition dispersed in liquid particle form in this emulsion is then cured by dispersing the emulsion in hot water.
In another example, Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 62-257939 (257,939/1987)/U.S. Pat. No. 4,761,454, teaches a process in which (i) an organopolysiloxane having at least two silicon-bonded alkenyl groups in each molecule, and an organopolysiloxane having at least two silicon-bonded hydrogen atoms in each molecule, are emulsified using water and a surfactant; (ii) a platinum catalyst is added to the emulsion; and (iii) the curable silicone composition dispersed in liquid particle form in the emulsion is then cured by heating or spray drying the emulsion.
In the former process, i.e., U.S. Pat. No. 4,742,142, however, curing occurs in the curable silicone composition prior to its homogeneous dispersion in water. This causes problems such as the production of cured silicone powder with a broad particle size distribution, and the presence in the cured silicone powder of a substantial amount of large gel particles.
The latter process, i.e., U.S. Pat. No. 4,761,454, while not suffering from the problems described in U.S. Pat. No. 4,742,142, does require an extended period of time to achieve an acceptable cure, because the rate of incorporation of the platinum catalyst into the organopolysiloxane emulsion is rate-determining for the process. As a result, the process in U.S. Pat. No. 4,761,454 has poor productivity. In addition, since the emulsion breaks during the extended period of time required for curing, problems of a broad particle size distribution and the presence of large gel particles again arise.